The present invention relates to improved oil based compositions for temporarily sealing subterranean zones and methods of utilizing the compositions.
In the drilling of oil and gas wells using the rotary drilling method, drilling fluid is circulated through the drill string and drill bit and then back to the surface by way of the well bore being drilled. The drilling fluid maintains hydrostatic pressure on the subterranean zones through which the well bore is drilled and circulates cuttings out of the well bore. During such drilling, subterranean vugs, fractures, and other thief zones are often encountered whereby the drilling fluid circulation is lost, and drilling operations must be terminated while remedial steps are taken. Also, when a subterranean zone is penetrated containing fluids under pressure which exceeds the hydrostatic pressure exerted on the zone by the drilling fluid, formation fluid crossbows and/or underground blow-outs can and often do occur. As a result, drilling fluid circulation is often lost which requires the termination of the drilling and the implementation of remedial procedures which are often of long duration and high cost.
U.S. Pat. No. 6,060,343 issued May 9, 2000 having inventors Ronald E. Sweatman and James F. Heathman and issued to Halliburton Energy Services, Inc. describes oil based compositions and methods of using the compositions for sealing subterranean zones. The compositions are basically comprised of oil, a hydratable polymer, an organophilic clay, and a water-swellable clay. These compositions and methods develop ultra high viscosity in a few seconds or minutes, solving many problems associated with prior art methods and compositions, and have been highly successful for sealing subterranean zones. The specification of U.S. Pat. No. 6,060,343 is incorporated herein by reference in its entirety.
It is sometimes desirable, however, to temporarily seal a subterranean zone. Thus, there is a need for improved compositions and methods for sealing subterranean zones having the benefits and advantages of the compositions disclosed in U.S. Pat. No. 6,060,343 and that would have the additional benefit of temporarily sealing subterranean zones. After having been sealed for the desired well workover activity, it would be desirable to be able to easily and quickly reopen the subterranean zones. It would still be important, however, that such a seal not be easily washed out or removed until it is desired to remove the plug and reopen the zone.